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Internet Settings
After setting up a PS3 network connection, the PS3 automatically applies those settings when connecting to the Internet. If your Internet settings have changed recently, this will result in dropped connections and subsequent sign-outs. Verify that the Internet settings haven't been changed and run a connection test from the Network Settings menu on the PS3. If changes have been made, edit the appropriate settings and retest the connection.
Router Interference
The quality of your router may be responsible for the frequent sign outs. The PS3 requires that your router support 802.11b or 802.11g signals. Other devices, such as microwaves and other wireless equipment, can cause interference that will result in dropped connections, so move the router away from such devices. If the router is too far away from the PS3, the signal may be weak and unstable, so move the router closer to the PS3.
ISP Issues
If you're being signed out of the PlayStation Network, your ISP may be responsible. Common broadband connections such as DSL and cable aren't 100 percent reliable and may disconnect from time to time for various reasons. Disconnections are most common during peak hours, when many users of the same ISP are online in your area. Avoid using the PS3 online during peak hours.
PlayStation Network Outage
The PlayStation Network unexpectedly goes down occasionally, causing you to be disconnected. Although this shouldn't happen repeatedly, it's not uncommon. If the PlayStation Network is undergoing maintenance, a message will be displayed in the notification bar on the PS3 and on the official PlayStation website.